Construction, Equivalent circuit, Principle of Operation, Solved Example Problems
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• The crystals are either naturally occurring or synthetically manufactured, exhibiting the piezoelectric effect. The piezoelectric effect means under the influence of the mechanical pressure, the voltage gets generated across the opposite faces of the crystal.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• For an oscillator, the frequency of the oscillations must remain constant. The analysis of the dependence of the oscillating frequency on the various factors like stray capacitance, temperature etc. is called as the frequency stability analysis.
Construction, Principle of Operation, Advantages, Equivalent Circuit, Solved Example Problems
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• In Hartley and Colpitt's oscillator, the frequency stability is poor because, i) The transistor internal capacitance affects the of feedback network equivalent value capacitance. ii) The transistor parameters depend on temperature which changes its internal capacitance and affects the frequency.
Types, Transistorised, Derivation of Frequency, Advantages, Disadvantages, Applications, Equivalent Circuit, Solved Example Problems
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• It uses two capacitive reactances and one inductive reactance in its feedback network. It is also classified as, i) BJT Colpitt's oscillator ii) FET Colpitt's oscillator.
Transistorised, Derivation of Frequency, Advantages, Disadvantages, Applications, Equivalent Circuit, Solved Example Problems
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• It uses two inductive reactances and one capacitive reactance in its feedback network. Depending on the active device used in amplifier stage, the two types of Hartley oscillators are, i) BJT Hartley oscillator ii) FET Hartley oscillator.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• An amplifier stage provides 180° phase shift while the feedback network contributes additional 180° phase shift to satisfy Barkhausen condition.
Principle of Operation
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• The oscillators which use the elements L and C to produce the oscillations are called LC oscillators. The circuit using elements L and C is called tank circuit or oscillatory circuit, which is an important part of LC oscillators.
Derivation of Frequency, Advantages, Disadvantages, Comparison, Solved Example Problems
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• The Wien bridge oscillator is also an RC oscillator which uses Wien bridge circuit as its feedback network.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• It consists of an amplifier and feedback network consisting of resistors and capacitors.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• The Fig. 10.4.1 gives the overall classification of oscillators.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• For an oscillator, there is no input (Vs = 0) hence feedback voltage Vf must be sufficient to maintain the oscillations.
Subject and UNIT: Electron Devices and Circuits: Unit V: (b) Oscillators
• Thus the input and feedback voltage i.e. Vs and Vf are in phase hence it is called positive feedback.